Methods for forming a thin film on an object can be generally divided into Physical Vapor Deposition (PVD) methods, such as sputtering, in which a thin film is formed in such a way that the physical properties of a deposition source and the physical properties of a thin film material are identical, and Chemical Vapor Deposition (CVD) methods, in which a thin film is formed using a chemical reaction in such a way that the physical properties of a deposition source and the physical properties of a thin film material are different.
However, The CVD methods are more commonly used because the PVD methods have the uniformity of composition or thickness and the step coverage that are not as good as those of the CVD methods. The CVD methods include the APCVD (Atmospheric Pressure CVD) method, the LPCVD (Low Pressure CVD) method, the PECVD (Plasma Enhanced CVD) method, etc.
Among the CVD methods, The PECVD method has been recently used widely, owing to its capabilities of low temperature deposition and fast forming of a thin film. The PECVD method refers to a method in which RF power is applied to reaction gas injected into a reaction chamber to make the reaction gas in a state of plasma and radicals in the plasma are made to be deposited on a wafer or glass substrate.
No matter which method is adopted, uniform deposition of thin film is the most key to a thin film deposition process, and thus a large number of improvement ideas have been suggested for this. For uniform deposition of thin film, uniform distribution of reaction gas or plasma plays a very important role.
A PECVD apparatus is equipment that is indispensable in a thin film process, and the scale of the PECVD apparatus has been gradually increasing due to the large scales of required yield. For instance, the PECVD apparatus used in a recent process for manufacturing flat-screen display devices is extra-large with the size of one side being easily over 2 meters, and thus it is required that its detailed functions be configured to be more precise in order to obtain a thin film of a desired quality.
The present invention suggests ideas for improving the function of spraying the gas and minimizing the warping phenomenon caused by thermal expansion of a gas spray surface, in order to make the thickness of a thin film uniform inside a PECVD apparatus for manufacturing a large-surface thin film.
FIG. 1 illustrates a brief configuration of a general PECVD apparatus, and described below with reference to FIG. 1 are processes using the PECVD apparatus.
First, once a substrate 3 is safely received on an upper surface of a susceptor 2, which is installed inside a reaction chamber 1, by a robot arm (not shown), gas for a thin film process enters and is diffused in a buffer space 5, which is located above a shower head 4, through a gas inlet pipe 7. The gas diffused in the buffer space 5 is uniformly sprayed over the substrate 3 through spray nozzles 4a of the shower head 4, and the sprayed gas is transformed to a state of plasma 8 by RF (Radio Frequency) power that is supplied through a plasma electrode 6. The reaction gas in the state of plasma 8 is deposited onto the substrate 3, and any reaction gas remaining after completion of the thin film deposition process is discharged through an outlet pipe 9 by a vacuum pump (not shown).
However, as shown in FIG. 2, the shower head 4 in the PECVD apparatus has a problem of sagging in the middle due to its own weight and thermal deformation. The thermal deformation is caused by thermal expansion due to heat transfer from the high-temperature plasma and a heater (not shown) installed in the susceptor 2, and the thermal expansion is greater in horizontal directions than in vertical (thickness) directions.
When the middle of the shower head 4 is sagged and thus warped, the distance between the shower head 4 and the susceptor 2 becomes closer in the middle than in the peripheral areas, making the distribution density of the sprayed gas ununiform and deteriorating the process uniformity.